1. Field of the Invention
The present invention relates to a hemming apparatus and more particularly to an apparatus for hemming the peripheral part of a work piece in the form of a door, a bonnet or the like usable for a motorcar.
2. Description of the Prior Art
To facilitate understanding of the present invention, it will be helpful that a conventional hemming apparatus will be described with reference to FIG. 7 which illustrates an example of an apparatus for hemming the peripheral part of a work such as a door, a bonnet or the like usable for a mortorcar. Referring to the drawing, a lower die half 61 includes a hemming die 63 on which a work W conveyed by conveying means (not shown) is set. In addition, it includes a york 66 which is supported turnable about a shaft 65 secured to a bracket 64 fixedly mounted on a base board 62.
In the drawing, reference numeral 68 designates an upper die half in which a movable frame 69 is slidably accomodated. The movable frame 69 is provided with a presser 70 for firmly holding the work W. Additionally, a main bending punch 72 extending in parallel with the presser 70 is secured to the lower end surface of a die holder 71 made integral with the upper die half 68, and moreover a cam 73 adapted to come in engagement with a cam follower 66a during lowering movement of the upper die half 68 is secured to the lower end surface of the die holder 71. Incidentally, reference numeral 74 designates a spring which imparts a thrusting force to the presser 70 under the effect of compression during lowering movement of the upper die half 68, reference numeral 75 does a pin which serves for operatively connecting the movable frame 69 to the upper die half 68 while preventing the movable frame 69 from falling from the upper die half 68, reference numeral 76 does a member made integral with the movable frame 69 for firmly holding the work W during hemming operation, reference numeral 77 does a pin and reference numeral 78 does a guide member for guiding upward and downward movements of the movable frame 69.
With such construction, when the upper die half 68 is lowered by operating pressing means (not shown), the peripheral parts W of two sheet-shaped works W of which edges are superposed one above another are firmly held by the presser 70 which has been lowered. Thereafter, a series of pressing operations are performed in accordance with the order of forward movement of the preliminary bending punch 67 for the purpose of preliminary bending, backward movement of the same and lowering movement of the main bending punch 72 for the purpose of final bending operation.
As will be apparent from the above description, the conventional hemming apparatus is divided into the upper die half and the lower die half to assure that a work is placed on the upper surface of the lower die half, and the upper die half is lowered onto the lower die half. Indeed, the upper die half is provided with a presser and a main bending punch and the lower die half is provided with a preliminary bending punch. The preliminary bending punch is constructed to operate under the effect of engagement with a cam mechanism secured to the upper die half. Further, a timing for hemming operations to be performed is set in view of a mechanical connective relationship among the presser, preliminary bending punch and main bending punch. Due to such construction as mentioned above, the conventional apparatus has drawbacks that it becomes complicated in structure, it is made at an expensive cost, there is a need of providing work conveying means adapted to move in and out of a clearance between both the upper and lower die halves, and it is restricted with respect to configuration, dimensions, operation timing and others. Another drawback is that it is difficult to adjust a timing with respect to the presser, preliminary bending punch and main bending punch.